Operating power factors

Several factors are important in the performance of a generator, and not the service conditions alone, as discussed for motors, in Section 1.6. In addition to service conditions, the operating power factor plays a significant role in the selection of a DG set, as noted above. The following p.f. conditions may occur in practice, depending upon the type of loads connected on the system. Refer to Figure 16.8. 

Assume the plant p.f. before the power factor correction to be 0.65. (We have provided in Table 23.8 the likely operating power factors for different types of industries, as a rough guide.) It this p.f. is to be improved to say, 0.95. then from Table 23.6,... 

Table 23.8 Likely operating power factors for different types of industries...

Operating power factors before the disturbance is applied. 

Dependable Capacity - The load-carrying ability of an electric power plant during a specific time interval and period when related to the characteristics of the load to be/being supplied determined by capability, operating power factor, and the portion of the load the station is to supply. 

Power factor correction The practice of placing or connecting one or more devices (usually capacitors) onto an AC power circuit in order to improve its operating power factor. 

Power factor indicates the degree to which a customer s electrical equipment causes the electric current delivered to the site to lag or lead with the voltage sine wave in other words, it is a measure of how much reactive power the equipment requires to operate. Power factor is calculated by using metered measures of the amount of power used (in kilowatts) and the amount of reactive power used (in kilovolt-amperes—kVA). Lower power factors indicate the use of greater amounts of reactive power. 

Power Supplies and Controls. Induction heating furnace loads rarely can be connected directiy to the user s electric power distribution system. If the load is to operate at the supply frequency, a transformer is used to provide the proper load voltage as weU as isolation from the supply system. Adjustment of the load voltage can be achieved by means of a tapped transformer or by use of a solid-state switch. The low power factor of an induction load can be corrected by installing a capacitor bank in the primary or secondary circuit. 

Active power factor correction circuits can take the form of nontransformer isolated switching power supply topologies, such as buck, boost, and buck/boost. The buck topology in Figure C-3 produces an output dc voltage lower than found at its input, whenever the PFC stage is operating (F > Fom). In other... 

Determination of Reliability Characteristic Factors in the Nuclear Power Plant Biblis B, Gesellschaft fur Reaktorsicherheit mbH Nuclear Failure rates with upper and lower bounds and maintenance data for 17,000 components from 37 safety systems Data for pumps, valves, and electrical positioning devices, electric motors and drives from an operating power plant 66. 

Aside from the efficiency of the motor itself, energy efficiency is very dependent upon proper sizing. While the efficiency of a motor is fairly constant from full load down to half load, when a motor operates at less than 40 percent of its full load, efficiency drops considerably, since magnetic, friction, and windage losses remain fairly constant regardless of the load. Moreover, the power factor drops continuously as... 

Figure 14-13 illustrates the power factor operation of various types of equipment. 

The induction motor usually requires irom 0.3 to 0.6 reactive magnetizing kva per hp of operating load, but an 0.8 leading power factor synchronous motor will deliver from 0.4-0.6 corrective magnetizing kva per hp depending on the mechanical load carried. Thus, equal connected hp in induction and 0.8 leading power factor synchronous motors will result in an approximate unity power factor for the system. 

Figure 14-13. Power factor operation of various apparatus and how synchronous motors improve power factor. (Used by permission E-M Synchronizer, 200-SYN-42, 1955. Dresser-Rand...

Motor Torque, 651 Power Factor for Alternating Current, 652 Motor Selection, 653 Speed Changes, 654 Adjustable Speed Drives, 659, Mechanical Drive Steam Tmbines, 659 Standard Size Turbines, 661 Applications, 662 Mtyor Variables Affecting Turbine Selection and Operation,... 

Synchronous generator type is in use for all generating applications up to the highest ratings (660 MW and above). The machine is operated at synchronous speed and the terminal voltage and power factors of operation are controlled by the excitation. 

This chapter introduces the basic items of design and specification for the principal systems and components of an electrical industrial installation. Electrical supply systems are discussed with regard to interface with the supply authorities and the characteristics. Salient features of switchgear, transformers, protection systems, power factor correction, motor control equipment and standby supplies are identified and discussed together with reference to the relevant codes of practice and standards. The equipment and systems described are appropriate to industrial plant installations operating at typically 11 kV with supply capacities of around 20MVA. 

Power factor in an alternating current circuit is defined as the ratio of actual circuit power in watts (W) to the apparent power in voltage amperes (VA). The need for correction arises from fact that the majority of A.C. electrical loads take from the supply a lagging quadruple current (voltage amperes reactive, var) and thus operates at a lagging power factor due to the reactive (rather than capacitive) nature of their construction. 

All these types of load fall into the above category and operate at a lagging power factor. 

The power factor of an installation can be improved by the use of either A.C. synchronous machines or of static capacitor banks. An A.C. synchronous machine will either draw current from the supply or contribute current to the supply, depending on whether the machine is operating ... 

When an A.C. synchronous machine operating as a motor in parallel with other loads and an external supply system is over-excited the machine will contribute reactive kvar to the supply. The net effect of this will be to reduce the amount of reactive current drawn from the supply, and this will improve the overall system power factor. 

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